PROJECT SUMMARY Immune checkpoint blockade (ICB) has improved outcomes for patients with various malignancies by disinhibiting anti-tumor T cells; however, most cancer patients do not yet benefit from it. In situ vaccination (ISV), which converts tumors into therapeutic vaccines via direct intratumoral treatment, is under investigation as a means of potentiating ICB. ISV often consists of injecting tumors with agents that activate stimulatory receptors on antigen presenting cells (APCs). However, this method of ISV has not yet been translated into standard-of-care treatments for most cancer patients. This may be, in part, because of the secretion of inhibitory cytokines such as IL10 that confer negative feedback in response to ISV, and thus represent a critical barrier to progress in this field. Preliminary data in this proposal suggest that by incorporating an IL10 receptor- blocking antibody (?IL10R) into ISV, tumor control is significantly improved. These data further suggest that ?IL10R enhances tumor control by two distinct mechanisms, and support the central hypothesis that ?IL10R enhances innate immune cells' ability to control tumors, in various in situ vaccines, by both a direct and an indirect mechanism. The objective of this proposal is to interrogate this central hypothesis through the proposed Specific Aims. This work will provide ideal training for the candidate as he prepares for his long-term career goal of investigating the mechanisms by which innate immune cells can enhance the efficacy of cancer immunotherapy. Memorial Sloan Kettering Cancer Center has a renowned immunology program. Dr. Jedd Wolchok, the candidate's mentor, is a leader in the development of new immunotherapies, and the candidate's co-mentors are experts on distinct aspects of innate immune cell biology. All have strong track records of mentoring independent scientists. Together with the candidate and an interdisciplinary advisory committee, they have formulated a rigorous training plan designed to increase the candidate's knowledge base in (i) innate immunity, (ii) bioinformatics, especially regarding single-cell data, (iii) statistics, and (iv) practical skills related to professional development. Training in these areas will occur through formal coursework, workshops, and meetings with mentors and the advisory committee, who will evaluate the candidate's progress. This research project and training plan will provide the foundation for the candidate to transition to a tenure-track position leading an academic laboratory that is well positioned to compete for R01 funding. The candidate's ultimate aim is to define new ways to enhance immunotherapy through the innate immune system, and thereby extend life for patients with a range of solid cancers.